The present invention relates to heating, ventilating, and air-conditioning (HVAC) equipment, systems, and methods.
Perhaps the most widely accepted HVAC system on the market today is the variable air volume (VAV) system. This system utilizes a large central air-handling unit and large ducts to deliver heated or cooled primary air to remote terminal boxes or zones. These boxes are thermostatically controlled to provide the volume of air required to maintain the zone at a desired temperature, or within a desired temperature range. Perimeter spaces (i.e., those spaces proximate exterior walls) have some form of radiation or secondary heating and cooling systems to compensate for thermal transmission through the exterior walls.
VAV systems are generally energy efficient, have a reasonable first cost, and are relatively easy to maintain and operate. However, these systems also have their disadvantages. First, VAV systems have a relatively high operating cost. Because all cooling requirements are met by a central air handling unit, relatively large fans and ductwork are required to move the large volume of air required. These large fans are relatively expensive to operate, and the large ducts are relatively expensive to construct and require a great deal of building volume. Further, VAV systems have many months when both heating and cooling equipment must be operated simultaneously to properly regulate the temperature of all zones within the structure. Obviously, this is a wasteful use of energy.
As is well-known to those skilled in the art, the interior area of a structure remote from the exterior walls contains an excess of heat generated, for example, by people, lights, and equipment. Consequently, these interior spaces must be cooled during much of the heating season, as well as during the cooling season. VAV systems typically blow this excess heat out of the building rather than making an attempt to reclaim the heat.
Further, VAV systems are extremely difficult to apply without violating regulations promulgated by government. Typically, VAV systems require daily adjustment of both equipment and thermostats to meet, in particular, the Emergency Temperature Regulations.
Additionally, air is throttled by VAV systems to properly regulate the temperature of the separate zones. This throttling of air flow can result in inadequate ventilation and also a "dead air" feeling.
Finally, VAV systems require many man hours to test and balance. Generally speaking, any one portion of the system is not balanced until all of the other portions are balanced.
Typically, VAV perimeter heating is supplied using fin tubing which provides convection heating. Other secondary heating and cooling systems used in conjunction with VAV systems include fan/coil units and induction units. Fan/coil units include a casing, a fan for moving air through the casing, and heating and/or cooling coils to warm or cool the air moving through the unit, as necessary. However, these units merely recirculate existing room air and do not provide for introducing outside air into the building at the unit.
On the other hand, induction units include a casing, structure for jetting primary air out of the casing thereby inducing room air to circulate through the casing, and heating and/or cooling coils to warm or cool the air moving through the unit, as necessary. Although induction units provide for the introduction of primary air, this is accomplished through relatively high pressure primary air supply systems, which are both complex and expensive.